This type of supporting roller stand serves to support very broad casting strands, i.e. over one meter, e.g. 2100 mm and more, so that bulging of the strand due to ferrostatic pressure in the interior of the strand which is only cooled externally, may be avoided. This type of supporting roller stand requires measurements which will keep within permissible limits any bending of the supporting rollers which are excessively long in accordance with the great width of the strand. Furthermore, it must be insured that the engaging surfaces of the supporting rollers do not inflict any damage on the strand surface such as grooves, tears, or the like.
It was disclosed by German Publication DF-AS No. 1 458 158 to make the diameter of the supporting rollers large enough to withstand ferrostatic pressure with slight bending. However, a large supporting roller diameter results in a wide distance from roller axis to roller axis so that the strand shell may bulge between two supporting rollers. On the other hand, the diameter of the supporting rollers connot be chosen extremely small, either, as this would permit excessive bending of the supporting rollers. The prior art deals with this difficulty by staggering the rollers whereby the end rollers with half the ball or strand engaging surface length are alternately arranged at one axis end each, and each axis is, at its end and between individual rollers, held by axis supports resting on a rear beam. The beams, in turn, rest on a stationary frame. The staggered arrangement of the rollers eliminates grooves in the strand surface as each gap between two supporting rollers on aligned axes is followed by a smooth roller ball or engaging surface of a staggered supporting roller of the neighboring axis which will smooth out already existing grooves, if any. Furthermore this suggestion permits, in view of the rear beam and in conjunction with the stationary frame, to make the diameters of the supporting rollers smaller so that the rollers may be spaced closer together than was previously the case.
The example of the disclosed suggestion shows, however, that the diameters of the supporting rollers are conventionally adapted to the thickness of the strand shell. This results in the familiar group arrangement of the supporting rollers, their diameters increasing from group to group. The increase in the supporting roller diameter by groups serves to increase drive torque which may be applied to a greater degree with increasing thickness of the strand shell. The roller diameter increase by groups further means that in the area where the strand shell is at its thinnest--near the strand casting chill--the diameter of the rollers is small, and where the strand shell is of medium thickness the rollers are provided with medium diameters, and where the strand shell is thick the rollers, too, have the greatest diameters. The known suggestion therefore follows the usual increase in diameter relative to the growing strand shell thickness and cannot make use of the advantage of a bending-resistant supporting roller with greater diameter. This disadvantage is necessarily compensated for by the rear beam in conjunction with the stationary frame.
The present invention is based on the design mentioned initially, e.g. a supporting roller stand with subdivided supporting rollers which are of different lengths and which are arranged in groups of different diameters.
The purpose of the invention is to eliminate bulging of the strand shell in broad slab steel strand casting plants in all solidification areas by using relatively large supporting roller diameters and to simultaneously maintain small distances between rollers, and furthermore to avoid any formation of grooves or similar damages to the surface of the cast strand.
The invention solves this by providing the supporting rollers successively with one smaller and one larger diameter and by arranging next to each supporting roller with large diameter two or more supporting rollers with smaller diameter, on one axis, whereby the combined strand surface engaging length of the supporting rollers with smaller diameter has a greater supporting length than the length of the solid supporting roller with larger diameter. Depending upon the difference in size chosen for the supporting rollers of smaller and larger diameter, provision is made between two supporting rollers of larger diameter for one supporting roller of smaller diameter which avoids any bulging in the area between two supporting rollers arranged at some distance. Supporting rollers of larger diameter may therefore be placed at such intervals that the supporting rollers of smaller diameters including their bearings find room between two supporting rollers of larger diameter.
The invention then avoids the requirement of supporting rollers of large diameter which, given sufficient length, would bend excessively, and also avoids bending of supporting rollers with reduced large diameter. The invention does make it possible to keep a relatively large diameter smaller for economical reasons. The basic concept of the invention does not make it necessary to dimension the supporting rollers with large diameter so that their length is greater than or as great as the width of the cast strand.
The supporting rollers of smaller diameter support the entire width of the cast strand due to the sum of their strand surface engaging lengths on one axis made up of several aligned individual coaxial rollers, whereby the supporting rollers of smaller diameter may even be longer than the width of the cast strand. On the other hand, the supporting rollers of large diameter may be kept shorter, thus eliminating the problem of sagging. The supporting rollers with smaller diameter have two functions. One, they avoid bulging between two supporting rollers with large diameter, and secondly they support areas over the width of the cast strand which are not covered by the supporting rollers with large diameter.
Those areas covered by the supporting rollers of smaller diameter result when, as provided by the invention, the length of the supporting rollers of larger diameter is even with or shorter than the strand width. In case the length of supporting rollers with larger diameter is even with the strand width, the supporting rollers of smaller diameter protrude past the edge of the strand and protect possibly uneven widths of the cast strand.
The principal advantage of the invention, i.e. the shortening of large diameter supporting rollers which are subject to bending stress is particularly useful if the length of the supporting rollers with large diameter decreases with increasing distance from the strand casting chill. This measure is based on the fact that the cast strand's tendency towards bulging decreases as strand shell thickness increases and the purpose of the supporting rollers with large diameter is not so much to support the strand but to transmit traction force to the cast strand. Generally it is advantageous to arrange the supporting rollers of large diameter in the center of the strand width which simultaneously insures symmetrical transmission of extraction forces over the width of the strand.
Furthermore, it is advantageous to provide only supporting rollers of larger diameter with a rotary drive. On one hand, the large supporting roller consisting of one piece is suitable for the transmission of a considerable torque and it requires only one drive. On the other hand the subdivided supporting rollers would require two drives in view of the fact that the motive force is to be transmitted symmetrically to the cast strand. Advantageous is also the central drive effect of the solid supporting rollers due to the greater ferrostatic pressure in the center of the cast strand width as it governs the effect of the drive. In general, it is advisable to synchronize the supporting rollers with larger diameter with the optimum strand width in accordance with the permissible degree of sagging. Furthermore, the invention allows greater length for supporting rollers with larger diameter in the area of liquid strand core than for the same supporting rollers in the area of semi-soft or completely solidified strand core.
Reference is made to the following illustrated embodiments of the invention as applied to a curved slab strand casting plant.